In between 2.5.56 and 2.5.57 IO speeds have dropped if CONFIG_PREEMPT is set.

The machine is a 4 processor Xeon with 8GB of RAM. The external storage isattached to the machine via qlogic 2200 HBAs using the qlogicfc driver. The filesystems on the external devices is reiserfs, mounted with noatimeas the only change from defaults. The config file is attached below. Thesame config was used for both 2.5.56 and 2.5.57. The config haspreemptable kernel enabled. I know preemption will lower your throughput,but it was enabled in 2.5.56, and speed was good.

The test involved the simultaneous writing to all 8 filesystems on the external storage. On 2.5.56, the vmstat output is below